Do you need antibiotics after a tick bite?

If the tick you pulled off was still flat, it's unlikely to have passed Lyme disease on.¹ Lyme bacteria live in the tick's gut. They move into its saliva only after the tick has fed for a while, which is why in most cases it has to be attached for more than 24 hours to spread Lyme.¹² A tick that's swollen with blood has fed longer, and that's worth telling a clinician.¹ Even so, Lyme can sometimes pass in less than a day.²

A single dose of the antibiotic doxycycline is worth asking a clinician about when four things line up.¹ The tick was a blacklegged (deer) tick, the small, teardrop-shaped kind and the only tick that spreads Lyme in the United States.³ It was swollen, or on for 36 hours or more.¹ It came off within the last 72 hours.¹ And you were somewhere Lyme is common, mainly the Northeast, mid-Atlantic and upper Midwest, with smaller pockets on the Pacific Coast.⁴ Can't tell what kind of tick it was? Ask anyway.¹ In the main trial, one dose cut the rate of Lyme rash from about 3 in 100 to under 1 in 100.⁵ It's considered safe for children of any age; the risks in pregnancy are less clear-cut, so talk it through with your clinician.¹ Otherwise, watch and wait.¹

A preventive dose is for Lyme alone. There's no good evidence it prevents Rocky Mountain spotted fever, anaplasmosis, ehrlichiosis or other tick-borne infections, and even for Lyme it isn't a guarantee.¹ Do not wait out a fever or headache 3 to 12 days after a tick bite: Rocky Mountain spotted fever, spread by dog ticks and Rocky Mountain wood ticks, can be fatal within days without early treatment.⁶

Either way, watch the bite for the next month.¹ Testing the tick won't help: a result can't guide treatment, and a negative one can falsely reassure you, since a different tick may have bitten you unnoticed.⁷ A small red bump that shows up right away, like a mosquito bite, is common and usually fades in a day or two. That isn't Lyme.⁸ The Lyme rash starts 3 to 30 days later and keeps spreading over several days, sometimes to 12 inches or more across.² It doesn't always look like a bull's-eye.² Fever, chills, headache, tiredness, aches or swollen glands can come with the rash or without it.² See a clinician for any rash or fever within 30 days of the bite.¹